A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103, which in turn vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. The cochlea 104 includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The scala tympani forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid filled cochlea 104 functions as a transducer to generate electric pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain. Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104.
In some cases, hearing impairment can be addressed by a cochlear implant that electrically stimulates auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along an implant electrode. FIG. 1 shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processing stage 111 which implements one of various known signal processing schemes. The processed signal is converted by the external signal processing stage 111 into a digital data format, such as a sequence of data frames, for transmission into a receiver processor in an implant housing 108. Besides extracting the audio information, the receiver processor in the implant housing 108 may perform additional signal processing such as error correction, pulse formation, etc., and produces a stimulation pattern (based on the extracted audio information) that is sent through wires in an electrode lead 109 to an implanted electrode array 110.
The electrode array 110 penetrates into the cochlea 104 through a surgical opening called a cochleostomy. The electrode array 110 has multiple electrode contacts 112 on or recessed slightly below its outer surface for applying one or more electrical stimulation signals to target audio neural tissue within the cochlea 104. The extra-cochlear electrode lead 109 that goes from the implant housing 108 to the cochleostomy opening usually has no electrical contacts except perhaps a ground electrode and it encloses connecting wires that deliver electrical stimulation signals to the electrode contacts on the electrode array 110.
After implantation, a cochlear implant system needs to be adjusted for each specific patient in a clinical fitting process. Information on patient performance while using the implant system is needed to compare different processing algorithms and/or processing parameters with regards to any differences in the performance of the system or the experience of the patient. This information can be obtained subjectively by feedback from the patient and/or by different objective measurement methods.